I played this all yesterday but gave up after spending forever on the last boss. Beat him in probably ten minutes this morning, typical.
Anyway I loved the game and would've gladly paid $15 for it, but being only $10 made it that much sweeter. The special powers are a lot of fun to use and I like the stealth and puzzle aspects to it. The top down perspective makes it reminiscent of classic Metal Gear Solid, and some of the puzzles are a little Portal-like in their execution. The game is structurally Metroid-like because more areas unlock as you gain new powers and give you access to more secret areas. Two types of collectibles, one of which is the in-game currency you use to upgrade your powers.
Some of the boss battles could be rather frustrating and I died A LOT but they fit nicely with the newly introduced mechanics. My first playthrough I was as pacifist as possible, which I'm glad that I did because now that I'm going through exploding everyone it's not as challenging (but exploding guys is a TON of fun).
My only criticisms are the occasional framerate issues and the challenge room unlocking ruins the pace of the game because you're forced to try each of them at least once when you discover/unlock them in game. Would've preferred the ability to save them for later.